content: /*
   * Copyright (C) 2009 The Guava Authors
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package io.dmitryivanov.crdt.helpers;
  
  import javax.annotation.Nullable;
  
  import java.util.Comparator;
  
  /**
   * A utility for performing a chained comparison statement. For example:
   * <pre>   {@code
   *
   *   public int compareTo(Foo that) {
   *     return ComparisonChain.start()
   *         .compare(this.aString, that.aString)
   *         .compare(this.anInt, that.anInt)
   *         .compare(this.anEnum, that.anEnum, Ordering.natural().nullsLast())
   *         .result();
   *   }}</pre>
   *
   * <p>The value of this expression will have the same sign as the <i>first
   * nonzero</i> comparison result in the chain, or will be zero if every
   * comparison result was zero.
   *
   * <p><b>Note:</b> {@code ComparisonChain} instances are <b>immutable</b>. For
   * this utility to work correctly, calls must be chained as illustrated above.
   *
   * <p>Performance note: Even though the {@code ComparisonChain} caller always
   * invokes its {@code compare} methods unconditionally, the {@code
   * ComparisonChain} implementation stops calling its inputs' {@link
   * Comparable#compareTo compareTo} and {@link Comparator#compare compare}
   * methods as soon as one of them returns a nonzero result. This optimization is
   * typically important only in the presence of expensive {@code compareTo} and
   * {@code compare} implementations.
   *
   * <p>See the Guava User Guide article on <a href=
   * "https://github.com/google/guava/wiki/CommonObjectUtilitiesExplained#comparecompareto">
   * {@code ComparisonChain}</a>.
   *
   * @author Mark Davis
   * @author Kevin Bourrillion
   * @since 2.0
   */
  public abstract class ComparisonChain {
    private ComparisonChain() {}
  
    /**
     * Begins a new chained comparison statement. See example in the class
     * documentation.
     */
    public static ComparisonChain start() {
      return ACTIVE;
    }
  
    private static final ComparisonChain ACTIVE =
        new ComparisonChain() {
          @SuppressWarnings("unchecked")
          @Override
          public ComparisonChain compare(Comparable left, Comparable right) {
            return classify(left.compareTo(right));
          }
  
          @Override
          public <T> ComparisonChain compare(
                  @Nullable T left, @Nullable T right, Comparator<T> comparator) {
            return classify(comparator.compare(left, right));
          }
  
          @Override
          public ComparisonChain compare(int left, int right) {
            return classify(Primitives.compare(left, right));
          }
  
          @Override
          public ComparisonChain compare(long left, long right) {
            return classify(Primitives.compare(left, right));
          }
  
          @Override
          public ComparisonChain compare(float left, float right) {
            return classify(Float.compare(left, right));
          }
  
          @Override
          public ComparisonChain compare(double left, double right) {
            return classify(Double.compare(left, right));
          }
  
          @Override
          public ComparisonChain compareTrueFirst(boolean left, boolean right) {
            return classify(Primitives.compare(right, left)); // reversed
          }
  
          @Override
          public ComparisonChain compareFalseFirst(boolean left, boolean right) {
            return classify(Primitives.compare(left, right));
          }
  
          ComparisonChain classify(int result) {
            return (result < 0) ? LESS : (result > 0) ? GREATER : ACTIVE;
          }
  
          @Override
          public int result() {
            return 0;
          }
        };
  
    private static final ComparisonChain LESS = new InactiveComparisonChain(-1);
  
    private static final ComparisonChain GREATER = new InactiveComparisonChain(1);
  
    private static final class InactiveComparisonChain extends ComparisonChain {
      final int result;
  
      InactiveComparisonChain(int result) {
        this.result = result;
      }
  
      @Override
      public ComparisonChain compare(@Nullable Comparable left, @Nullable Comparable right) {
        return this;
      }
  
      @Override
      public <T> ComparisonChain compare(
          @Nullable T left, @Nullable T right, @Nullable Comparator<T> comparator) {
        return this;
      }
  
      @Override
      public ComparisonChain compare(int left, int right) {
        return this;
      }
  
      @Override
      public ComparisonChain compare(long left, long right) {
        return this;
      }
  
      @Override
      public ComparisonChain compare(float left, float right) {
        return this;
      }
  
      @Override
      public ComparisonChain compare(double left, double right) {
        return this;
      }
  
      @Override
      public ComparisonChain compareTrueFirst(boolean left, boolean right) {
        return this;
      }
  
      @Override
      public ComparisonChain compareFalseFirst(boolean left, boolean right) {
        return this;
      }
  
      @Override
      public int result() {
        return result;
      }
    }
  
    /**
     * Compares two comparable objects as specified by {@link
     * Comparable#compareTo}, <i>if</i> the result of this comparison chain
     * has not already been determined.
     */
    public abstract ComparisonChain compare(Comparable<?> left, Comparable<?> right);
  
    /**
     * Compares two objects using a comparator, <i>if</i> the result of this
     * comparison chain has not already been determined.
     */
    public abstract <T> ComparisonChain compare(
        @Nullable T left, @Nullable T right, Comparator<T> comparator);
  
    /**
     * Compares two {@code int} values as specified by {@link Primitives#compare},
     * <i>if</i> the result of this comparison chain has not already been
     * determined.
     */
    public abstract ComparisonChain compare(int left, int right);
  
    /**
     * Compares two {@code long} values as specified by {@link Primitives#compare},
     * <i>if</i> the result of this comparison chain has not already been
     * determined.
     */
    public abstract ComparisonChain compare(long left, long right);
  
    /**
     * Compares two {@code float} values as specified by {@link
     * Float#compare}, <i>if</i> the result of this comparison chain has not
     * already been determined.
     */
    public abstract ComparisonChain compare(float left, float right);
  
    /**
     * Compares two {@code double} values as specified by {@link
     * Double#compare}, <i>if</i> the result of this comparison chain has not
     * already been determined.
     */
    public abstract ComparisonChain compare(double left, double right);
  
    /**
     * Discouraged synonym for {@link #compareFalseFirst}.
     *
     * @deprecated Use {@link #compareFalseFirst}; or, if the parameters passed
     *     are being either negated or reversed, undo the negation or reversal and
     *     use {@link #compareTrueFirst}.
     * @since 19.0
     */
    @Deprecated
    public final ComparisonChain compare(Boolean left, Boolean right) {
      return compareFalseFirst(left, right);
    }
  
    /**
     * Compares two {@code boolean} values, considering {@code true} to be less
     * than {@code false}, <i>if</i> the result of this comparison chain has not
     * already been determined.
     *
     * @since 12.0
     */
    public abstract ComparisonChain compareTrueFirst(boolean left, boolean right);
  
    /**
     * Compares two {@code boolean} values, considering {@code false} to be less
     * than {@code true}, <i>if</i> the result of this comparison chain has not
     * already been determined.
     *
     * @since 12.0 (present as {@code compare} since 2.0)
     */
    public abstract ComparisonChain compareFalseFirst(boolean left, boolean right);
  
    /**
     * Ends this comparison chain and returns its result: a value having the
     * same sign as the first nonzero comparison result in the chain, or zero if
     * every result was zero.
     */
    public abstract int result();
  }